Obesity is a disorder in which energy intake exceeds energy expenditure. Genetic differences are known to contribute to resting metabolic rage (RMR) and energy expenditure. UCP2 is a mitochondrial uncoupling protein (UCP) that is genetically linked to obesity and hyperinsulinemia in mice, and to RMR in humans. In vivo, the expression of UCP2 in adipose tissue is increased by high-fat diets in the obesity-resistant A/J strain of mice, but not in the obesity- prone C57BL/6J mice. Three hypotheses are made in this proposal: 1) that fatty acids or their metabolites regulate UCP2 gene transription in the A/J mouse; 2) that sequence elements in the UCP2 promoter control this dietary induction of the UCP2 gene, and 3) sequence differences in the UCP2 promoter exist between to A/J and B6 strains, and forms the basis for the QTL for obesity and diabetes to the UCP2 locus. To test these hypotheses, the sequence and functional activity of the A/J mouse will be determined. A series of UCP2 promoter deletions will be examined for functional activity in adipocyte cell lines. The ability of PPAR activators to increase promoter activity of the A/J UCP2 promoter constructs in adipocytes will be determined. The identity of UCP2 promoter elements that are responsive to these agents will be examined by DNA gel shift and super-shift assays. Finally, the UCP2 promoter from the B6 mouse will be compared to the A/J UCP2 promoter. These studies will define the sequence elements and mechanisms regulating the UCP2 gene. This comparison will determine whether sequence differences in UCP2 between these strains is the basis for the genetic linkage of obesity to this locus, and provide a molecular explanation for the physiological differences observed between these two strains in response to a high -fat diet.